Changed my water pump/thermostat recently ...2006 mazda3....water pump frozen in block had to physically break it into two/three pieces to get it out ...then had leak on the other side of the engine ...water outlet valve which I think must have cracked as it is plastic when binding on raising the engine to get at the water pump ...job took way more time and effort than it should have. If you change your pump definitely spend the $30 for the thermostat and do it while you are there.

 

If it were me, and it's not, I would just go ahead and replace both the water pump and the thermostat. First of all, you'll have to drain the coolant anyway to do either so why not just do both together? We're talking about a combined $60 in parts (rockauto). Whenever I do a 2.3 to 2.5 engine swap I automatically replace these. That being said, they are much easier to replace with the engine out of the car. Sometimes the water pump takes a bit of force to extract from the engine block, which will be the most challenging part of the task.

Once all your new parts are in, park the car on an upward slope, or use jack stands to get the front up as high as you can safely. With the radiator cap off, run the car until the thermostat is open and continuously monitor the temp gauge as well as the coolant level. Run your heater. If you feel hot air from the heater it is a very good sign that you have purged air from the system, and that you pump is circulating water appropriately.

Please do not risk your engine for $60 in parts. That is unless you want to learn how to do the 2.5 swap, which will surely become a necessity if you keep overheating your engine.

 

I got a P0125 code.

 

I suggest getting the correct coolant level in that reservoir and then following the air bleed/purge process. After or concurrently, you'll need to determine where that coolant went in the first place... (Based on the rust and residue at that hose clamp pictured, I'd closely examine every hose connection you see for weeps (after the coolant level is appropriately full). While a P0125 could be due to a number of causes, your low coolant level is either because of a leak or someone did a lousy job of re-filling after the thermostat job.

 

 

I don't have any check engine lights. I left the car running for some time, but haven't seen any coolant coming out from the water pump area or on the ground after. Tensioner looks like it's shaking a bit? Last owner said the thermostat was changed not too long ago. Coolant level is very low (check picture). I will get my obd-II scanner and do a test today.

 

Is the coolant level in the reservoir correct? No Check Engine light? (Did you run an OBD-II scan for pending codes, if no CEL?)

The water pump should be relatively easy of a repair (maybe most challenging to get the pulley off/on?); if you don't have much DIY experience, you may need to acquire some tools and go more slowly. That said, I think it's premature to say replacing that will fix your issue. I expect a failing water pump would have a noticeable leak from the weep hole, at least. It sounds more like a thermostat issue, but I'd want to evaluate for codes and coolant loss for more evidence.